Low-cost heliostatic mirror with protective inflation stabilizable surface element means

Abstract

Increased utilization of solar power is highly desirable as solar power is a readily available renewable resource with power potential far exceeding total global needs; and as solar power does not contribute to environmentally harmful pollutants associated with fossil fuel power, such as unburned hydrocarbons, NOx and carbon dioxide. The present invention is motivated by the fact that heliostats are the single biggest cost element for utility-scale central receiver solar thermal powerplants. This invention provides a low-cost heliostatic mirror with protective inflation stabilizable surface element means for providing adverse weather performance & survival, where the inflation stabilizable surface element means include inflation stabilizable near-spherical surface element means and may include inflation stabilizable near-cylindrical surface element means.

1. A low-cost heliostatic mirror with inflation stabilizable surface element means for providing adverse weather performance & survival, comprising:
 a mirror comprising thin reflective surface means for reflecting incident sunlight when the Sun is shining and visible; 
 heliostatic control means for angular pointing of said mirror so as to cause said mirror to reflect said incident sunlight to form a reflected sunlight beam going to a target region at which a solar receiver can be located; 
 perimeter support means for accurately setting and holding the perimeter of said thin reflective surface means in a desired orientation as commanded by said heliostatic control means; 
 inflation stabilizable surface element means for enhancing adverse weather performance & survival for said mirror, which inflation stabilizable surface element means include substantially transparent upper inflation stabilizable near-spherical surface element means located above an upper inflatable volume above the sunlight reflecting sunward side of said mirror, and lower inflation stabilizable near-spherical surface element means located below a lower inflatable volume below the nonsunward side of said mirror; 
 and 
 connecting lower perimeter encircling means and upper perimeter encircling means for encircling the lower perimeter of said lower inflatable volume and the upper perimeter of said upper inflatable volume respectively, which connecting lower perimeter encircling means and upper perimeter encircling means form a near-circular closed loop in circumferential tension when said lower inflated volume and upper inflatable volume are both fully inflated; 
 and wherein: 
 (a) said substantially transparent upper inflation stabilizable near-spherical surface element means and lower inflation stabilizable near-spherical surface element means together serve as means for enhancing adverse weather performance for said mirror under adverse weather conditions comprising winds below a 1 st  threshold level, when said upper inflatable volume and lower inflatable volume are fully inflated; 
 and wherein: 
 (b) said lower inflation stabilizable near-spherical surface element means serve as means for enhancing adverse weather survival for said mirror in a stowed survival configuration, under adverse weather conditions comprising at least one of severe winds below a 2 nd  threshold level, serious frozen precipitation below a 3 rd  threshold level and significant sandstorm particles below a 4 th  threshold level, when said lower inflated volume is fully inflated. 
 
     
     
       2. The low-cost heliostatic mirror of  claim 1 ,
 wherein said mirror comprising thin reflective surface means for reflecting incident sunlight, comprises upwardly concave thin reflective surface means for reflecting and concentrating said incident sunlight to form a to form a reflected sunlight beam that is narrowing reflected sunlight beam, and 
 wherein the target projected area of said target region that can receive said reflected sunlight beam, is less than the projected reflective area of said upwardly concave thin reflective surface means. 
 
     
     
       3. The low-cost heliostatic mirror of  claim 1 , wherein:
 a mirror comprising thin reflective surface means for reflecting incident sunlight comprises a reflective membrane with an upper reflective surface, and wherein said perimeter support means comprises at least one of a perimeter support frame and a substantially rigid perimeter support ring. 
 
     
     
       4. The low-cost heliostatic mirror of  claim 3 ,
 further comprising backing member means adjacent to the nonsunward side of said reflective membrane, for facilitating at least one of (i) maintaining a desired shape of the reflective membrane and (ii) damping motion of the reflective membrane. 
 
     
     
       5. The low-cost heliostatic mirror of  claim 1 , wherein:
 said inflation stabilizable surface element means are connected to said perimeter support means, and wherein said inflation stabilizable surface element means and said perimeter support means together form a near-spherical envelope surrounding said mirror when said upper inflatable volume and lower inflatable volume are fully inflated, 
 and wherein at least one of: 
 (i) said near-spherical envelope has a surface geometry that lies entirely within a volume defined by a true sphere's surface and regions within a 25% diameter distance of said true sphere's surface; 
 and 
 (ii) said near-spherical envelope has a surface geometry that serves as aerodynamic moment minimizing means for yielding relatively small aerodynamic moments responsive to wind applied from arbitrary angles on said surface geometry, wherein an aerodynamic moment is relatively small if the nondimensionalized aerodynamic moment coefficient per radian of angle of attack has a magnitude less than three halves. 
 
     
     
       6. The low-cost heliostatic mirror of  claim 1 , wherein:
 said inflation stabilizable surface element means comprise substantially gas-impermeable membrane members. 
 
     
     
       7. A low-cost heliostatic mirror with inflation stabilizable surface element means for providing adverse weather performance & survival, comprising:
 a mirror comprising thin reflective surface means for reflecting incident sunlight when the Sun is shining and visible; 
 heliostatic control means for angular pointing of said mirror so as to cause said mirror to reflect said incident sunlight to form a reflected sunlight beam going to a target region at which a solar receiver can be located; 
 perimeter support means for accurately setting and holding the perimeter of said thin reflective surface means in a desired orientation as commanded by said heliostatic control means; and 
 inflation stabilizable surface element means for enhancing adverse weather performance & survival for said mirror, which inflation stabilizable surface element means include 
 (i) substantially transparent upper inflation stabilizable near-spherical surface element means on lateral sides of substantially transparent upper inflation stabilizable near-cylindrical surface element means all located above an upper inflatable volume above the sunlight reflecting sunward side of said mirror, and 
 (ii) lower inflation stabilizable near-spherical surface element means on lateral sides of lower inflation stabilizable near-cylindrical surface element means all located below a lower inflatable volume below the nonsunward side of said mirror; 
 and wherein: 
 said (i) substantially transparent upper inflation stabilizable near-spherical surface element means on lateral sides of substantially transparent upper inflation stabilizable near-cylindrical surface element means and (ii) lower inflation stabilizable near-spherical surface element means on lateral sides of lower inflation stabilizable near-cylindrical surface element means, all together serve as means for enhancing adverse weather performance for said mirror under adverse weather conditions comprising winds below a 1 st  threshold level, when said upper inflatable volume and lower inflatable volume are fully inflated; 
 and wherein: 
 said (ii) lower inflation stabilizable near-spherical surface element means on lateral sides of lower inflation stabilizable near-cylindrical surface element means, together serve as means for enhancing adverse weather survival for said mirror in a stowed survival configuration, under adverse weather conditions comprising at least one of severe winds below a 2 nd  threshold level, serious frozen precipitation below a 3 rd  threshold level and significant sandstorm particles below a 4 th  threshold level, when said lower inflated volume is fully inflated. 
 
     
     
       8. The low-cost heliostatic mirror of  claim 7 , wherein
 the lateral width of said substantially transparent upper inflation stabilizable near-cylindrical surface element means is less than two times the effective diameter of said substantially transparent upper inflation stabilizable near-spherical surface element means; and wherein the lateral width of said lower inflation stabilizable near-cylindrical surface element means is less than two times the effective diameter of said lower inflation stabilizable near-spherical surface element means. 
 
     
     
       9. The low-cost heliostatic mirror of  claim 7 , further comprising:
 a lower perimeter member of near-circular arc form that is structurally contiguous to (i) a lower perimeter of said lower inflatable volume when said lower inflatable volume is fully inflated and to (ii) said perimeter support means at its upper ends; 
 and mirror support means for supporting said mirror on a ground surface which mirror support means includes a rotatable base member and connecting support means for supporting said lower perimeter member above said rotatable base member. 
 
     
     
       10. The low-cost heliostatic mirror of  claim 7 , further comprising:
 two lower perimeter members of near-circular arc form that are structurally contiguous to (i) lower perimeters of said lower inflatable volume when said lower inflatable volume is fully inflated and to (ii) said perimeter support means at its upper ends; 
 and mirror support means for supporting said mirror on a ground surface which mirror support means includes a rotatable base member and connecting support means for supporting said two lower perimeter members above said rotatable base member. 
 
     
     
       11. The low-cost heliostatic mirror of  claim 10 , wherein
 said two lower perimeter members comprise two substantially rigid lower perimeter members of approximately circular arc form, which two substantially rigid lower perimeter members of approximately circular arc form are each structurally connected at their upper ends to the lower ends of two corresponding substantially rigid upper perimeter members of approximately circular arc form, such that together they form two substantially rigid rings that surround an inflatable contiguous volume that includes both said lower inflatable volume and said upper inflatable volume; and wherein said connecting support means connects to and supports and restrains said two substantially rigid rings. 
 
     
     
       12. The low-cost heliostatic mirror of  claim 11 , wherein said two substantially rigid rings are designated as a left substantially rigid ring and a right substantially rigid ring, and further comprising:
 left loop means comprising at least one of a belt, a toothed belt, a belt with holes, a chain, and a concentric ring-bearing-connected member, that loops around both (a) the upper part of said left substantially rigid ring and (b) at least one left roller element connected to said rotatable base member; which left loop means serves as vertical restraint means for restraining said left substantially rigid ring from upward vertical movement; and 
 right loop means comprising at least one of a belt, a toothed belt, a belt with holes, a chain, and a concentric ring-bearing-connected member, that loops around both (a) the upper part of said right substantially rigid ring and (b) at least one right roller element connected to said rotatable base member; which right loop means serves as vertical restraint means for restraining said right substantially rigid ring from upward vertical movement. 
 
     
     
       13. The low-cost heliostatic mirror of  claim 7 , wherein said perimeter support means comprises a perimeter support frame, and wherein said perimeter support frame supports edges of each of: said substantially transparent upper inflation stabilizable near-spherical surface element means, said substantially transparent upper inflation stabilizable near-cylindrical surface element means, said lower inflation stabilizable near-spherical surface element means, and said lower inflation stabilizable near-cylindrical surface element means. 
     
     
       14. The low-cost heliostatic mirror of  claim 13 , wherein said perimeter support frame further provides perimeter edge support for said thin reflective surface means, which thin reflective surface means has a surface geometry that is close to the surface of a true sphere with a center at least one of: in and near said target region. 
     
     
       15. The low-cost heliostatic mirror of  claim 7 , wherein said mirror comprising thin reflective surface means for reflecting incident sunlight, comprises upwardly concave thin reflective surface means for reflecting and concentrating said incident sunlight to form a reflected sunlight beam that is a narrowing reflected sunlight beam, which upwardly concave thin reflective surface means has a near-spherical shape approximating the surface of a true sphere with radius R 1 ; wherein said substantially transparent upper inflation stabilizable near-spherical surface element means have near-spherical shapes approximating the surfaces of true spheres with radius R 2 ; wherein said substantially transparent upper inflation stabilizable near-cylindrical surface element means have near-cylindrical shapes approximating the surface of a true cylinder with radius R 3 ; wherein said perimeter support means comprises a perimeter support frame; wherein said perimeter support frame substantially supports edges of said substantially transparent upper inflation stabilizable near-spherical surface element means approximately along first geometric lines of intersection of said surface of a true sphere with radius RI on one hand, and said surfaces of true spheres with radius R 2  on the other hand; and wherein said perimeter support frame substantially supports edges of said substantially transparent upper inflation stabilizable near-cylindrical surface element means along second geometric lines of intersection of said surface of a true sphere with radius R 1  on one hand, and said surface of a true cylinder with radius R 3  on the other hand. 
     
     
       16. A low-cost heliostatic mirror with inflation stabilizable surface element means for providing adverse weather performance & survival, comprising:
 a mirror comprising thin reflective surface means for reflecting incident sunlight when the Sun is shining and visible; 
 heliostatic control means for angular pointing of said mirror so as to cause said mirror to reflect said incident sunlight to form a reflected sunlight beam going to a target region at which a solar receiver can be located; 
 perimeter support means for accurately setting and holding the perimeter of said thin reflective surface means in a desired orientation as commanded by said heliostatic control means; 
 inflation stabilizable surface element means for enhancing adverse weather performance & survival for said mirror, which inflation stabilizable surface element means include substantially transparent upper inflation stabilizable near-spherical surface element means located above an upper inflatable volume above the sunlight reflecting sunward side of said mirror, and lower inflation stabilizable near-spherical surface element means located below a lower inflatable volume below the nonsunward side of said mirror; 
 a lower perimeter member of near-circular arc form that is structurally contiguous to (i) a lower perimeter of said lower inflatable volume when said lower inflatable volume is fully inflated and to (ii) said perimeter support means at its upper ends; 
 and mirror support means for supporting said mirror on a ground surface which mirror support means includes a rotatable base member and connecting support means for connecting said lower perimeter member to said rotatable base member; 
 and wherein: 
 (a) said substantially transparent upper inflation stabilizable near-spherical surface element means and lower inflation stabilizable near-spherical surface element means together serve as means for enhancing adverse weather performance for said mirror under adverse weather conditions comprising winds below a 1 st  threshold level, when said upper inflatable volume and lower inflatable volume are fully inflated; 
 and wherein: 
 (b) said lower inflation stabilizable near-spherical surface element means serve as means for enhancing adverse weather survival for said mirror in a stowed survival configuration, under adverse weather conditions comprising at least one of severe winds below a 2 nd  threshold level, serious frozen precipitation below a 3 rd  threshold level and significant sandstorm particles below a 4 th  threshold level, when said lower inflated volume is fully inflated. 
 
     
     
       17. The low-cost heliostatic mirror of  claim 16 , wherein said heliostatic control means for angular pointing of said mirror includes both elevation control means for controlling the elevation angle of said mirror and azimuth control means for controlling the azimuth angle of said mirror; which elevation control means acts on at least one of said perimeter support means and said lower perimeter member; and which azimuth control means comprises rotational positioning means for rotationally positioning said rotatable base member. 
     
     
       18. The low-cost heliostatic mirror of  claim 16 , wherein said mirror support means further comprises two substantially coaxial pivot bearings connecting said perimeter support means to pivot support members, wherein the lower ends of said pivot support members are connected to and supported by said rotatable base member. 
     
     
       19. The low-cost heliostatic mirror of  claim 16 , wherein:
 said lower perimeter member of near-circular arc form comprises a substantially rigid lower perimeter member of approximately circular arc form, which substantially rigid lower perimeter member of approximately circular arc form is structurally connected at its upper ends to the lower ends of a substantially rigid upper perimeter member of approximately circular arc form, such that together they form a substantially rigid ring that surrounds an inflatable contiguous volume that includes both said lower inflatable volume and said upper inflatable volume; and wherein said connecting support means connects to and supports and restrains said substantially rigid ring at least one of (i) vertically and (ii) laterally. 
 
     
     
       20. The low-cost heliostatic mirror of  claim 19 , further comprising:
 loop means comprising at least one of a belt, a toothed belt, a belt with holes, a chain, and a concentric ring-bearing-connected member, that loops around both (a) the upper part of said substantially rigid ring and (b) at least one roller element connected to said rotatable base member; which loop means serves as at least one of (i) vertical restraint means for restraining said substantially rigid ring from upward vertical movement, and (ii) elevation control means for contributing to the elevation control part of said heliostatic control means.